1. Field of the Invention
The invention relates to an auxiliary power supply device including an auxiliary power source and an electric power steering system including the auxiliary power supply device.
2. Description of the Related Art
A conventional electric power steering system includes an auxiliary power source that is connected to a main power source, and a booster circuit that boosts a voltage of the main power source. In the electric power steering system, a boosted voltage of the booster circuit is applied to the auxiliary power source when the auxiliary power source is charged with the use of the main power source. Japanese Patent Application Publication No. 2009-166679 (JP 2009-166679 A) describes an example of a configuration of the conventional electric power steering system.
In the conventional electric power steering system, the relationship between the boosted voltage of the booster circuit and the voltage across terminals of a capacitor at the time of starting the charging of the auxiliary power source is not particularly considered in controlling the booster circuit. Accordingly, when the voltage across the terminals of the capacitor at the time of starting the charging of the auxiliary power source is higher than the boosted voltage of the booster circuit, an electric current may flow back from the capacitor to the booster circuit.